Summary
During the summer of 2008/09, measurements were taken at 34 magnetotelluric (MT) stations along profiles totaling approximately 180 line km in the Prydz Bay region of Antarctica. Prydz Bay comprises several regions of coastal outcrops with distinct geological histories, including the Vestfold Hills and the Rauer Group of islands. The primary aim of the MT survey was to image the boundary between the Vestfold Hills and the Rauer Group. The Vestfold Hills are dominated by 2520 – 2480 Ma orthogneisses that experienced granulite-grade metamorphism prior to 2470 Ma. They were intruded by several generations of dykes during the Paleoproterozoic and Mesoproterozoic. The Vestfold Hills have not been pervasively affected by high-temperature Neoproterozoic events, probably related to Gondwana amalgamation, that permeate much of the Prydz Bay region. The Rauer Group, which lies adjacent to the Vestfold Hills, preserves a significantly different geological evolution. The oldest rock package in the Rauer Group comprises 3300-2800 Ma tonalitic orthogneisses, layered igneous complexes and paragneisses. 1060-1000 Ma orthogneisses are interleaved with the Archean rocks in places, and the entire region is affected by 550-500 Ma metamorphism. The contrasting geological evolutions of the two regions suggest that they do not share a common history and were juxtaposed probably at either c. 1000 Ma or at c. 550-500 Ma during the amalgamation of Gondwana. The contact between the two regions is covered by the Sørsdal Glacier near the coast and by the Antarctic ice cap further inland and can therefore not be sampled directly. To image the contact, the MT survey was focused over the inland extension of the Sørsdal Glacier with station spacings of 2.5 km to 5km. Both broadband and long-period measurements were taken to constrain the structure from the near-surface to the upper mantle. MT is a passive electromagnetic geophysical technique which uses the earth’s time-varying magnetic field as its source field. It is applicable to Antarctic environments as its passive nature results in no environmental impact and since the frequencies contained in the source field enable signal penetration through thick ice. However, data collection in the Antarctic does pose several challenges. MT methodology assumes that the source field is a plane wave, with fluctuations in the vertical magnetic field only occurring due to lateral resistivity gradients in the earth. At locations close to the magnetic pole, this assumption may not hold. The vertical magnetic field was measured at most MT stations and these data were combined with permanent magnetic observatory data from the nearby Davis, Mawson and Casey stations to analyse the activity in the vertical magnetic field and the impact of this on the MT data. Electrical noise from statically charged ice particles blowing over the MT electrodes has been proposed to pose significant challenges to collecting high-quality MT data in polar regions. Weather data from the Woop Woop weather station, located at the northern end of the MT profile, were collected in order to compare wind speed and direction with electrical noise. Finally, the high contact resistance of ice poses a challenge to data collection and pre-amps were utilized to boost the signal collected at the electrode. Along-strike measurements were taken on ice-covered and ice-free regions to analyse the effects of ice on the measured signal.